A New Method for Leak Detection in Gas Pipelines

Kegang Ling, University of North Dakota; Guoqing Han and Xiao Ni, China University of Petroleum; Chunming Xu, China National Offshore Oil Corporation; and Jun He, Peng Pei, and Jun Ge, University of North Dakota | 25 February 2015

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Summary

Two types of approaches—physical inspection and mathematical-model simulation—are used to identify a leak in a gas pipeline. The former method can result in an accurate detection of the location and the size of the leak, but comes with the expense of production shutdown and the high cost/long time to run the physical detection, which is very crucial in a long-distance gas pipeline. The latter approach detects a gas leak by solving the governing equations, thus leading to quick evaluation at much lower costs, but with higher uncertainties. Our literature review indicates that a simple, practical, and reliable method to detect a gas leak under the conditions of unknown inlet or outlet gas rate, or unknown inlet or outlet pressure, is highly desirable.

In this study, we develop single and multiple rate test methods to detect leaks in a gas pipeline. By conducting multiple rate tests, the location and size of leaks can be detected. The new method can be applied under the conditions of no inlet or outlet rate available or no inlet or outlet pressure available. Because these conditions are not uncommon in gas-pipeline transportation, our method provides a quick and low-computational-cost approach to detect leaks corresponding to different scenarios.

Introduction

Because of its efficiency, cleanliness, and reliability, natural gas supplies nearly one-fourth of all energy used in the United States and is expected to increase by 50% within the next 20 years (Anderson and Driscoll 2000). New gas-delivery infrastructure is constructed to transport more natural gas to terminals far away from the production site. At the same time, existing gas-delivery infrastructure is aging rapidly. Ensuring natural-gas-infrastructure reliability is one of the critical needs for the energy sector. Therefore, the reliable and timely detection of leakage from a newly-built gas pipeline during startup, and the failure of any part of the old pipeline, is critical to the flow assurance of the natural-gas infrastructure.

Traditionally, there are two types of approaches to detecting leaks in a gas pipeline; one is physical inspection to identify the location and size of the leak, and the other is mathematical modeling with numerical simulation. Physical inspection consists of gas sampling; soil monitoring; flow-rate monitoring; and acoustic-, optical-, and satellite-based hyperspectral imaging. Usually, the physical inspection can result in an accurate detection of the location and size of a leak, but this comes with the expense of production shutdown and the high cost/long time to run the physical detection, which is very crucial in a long-distance gas pipeline. The mathematical-modeling approach detects a gas leak by solving the governing mass-conservation, momentum-conservation, and energy-balance equations, thus leading to a quick evaluation at much lower cost. It also has the advantages of monitoring the system continuously and noninterference with pipeline operations. One of the limitations of the modeling method is that it requires flow parameters, which are not always available. Leak detection from mathematical modeling also has a higher uncertainty than that from physical inspection.